Math Problem Statement

An architect is allowed 15 square yards of floor space to add a small bedroom to a house. Because of the room's design in relationship to the existing structure, the width of the rectangular floor must be 7 yards less than two times the length. Find the length and width of the rectangular floor that the architect is permitted.

Solution

We are tasked with finding the length and width of the rectangular floor. The total floor area is given as 15 square yards, and the width of the rectangular floor is defined as 7 yards less than twice the length.

Let's define the length and width in terms of a variable:

  • Let the length of the floor be LL yards.
  • The width of the floor is 2L72L - 7 yards (because it's 7 yards less than twice the length).

The area of a rectangle is given by the formula: Area=Length×Width\text{Area} = \text{Length} \times \text{Width} Substituting the given area and the expression for the width: 15=L×(2L7)15 = L \times (2L - 7) Now let's solve this equation:

Step 1: Expand the equation

15=L(2L7)15=2L27L15 = L(2L - 7) \Rightarrow 15 = 2L^2 - 7L

Step 2: Rearrange the equation into standard quadratic form

2L27L15=02L^2 - 7L - 15 = 0

Step 3: Solve the quadratic equation

We can solve this using the quadratic formula, where a=2a = 2, b=7b = -7, and c=15c = -15: L=b±b24ac2aL = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} Substitute the values of aa, bb, and cc: L=(7)±(7)24(2)(15)2(2)L = \frac{-(-7) \pm \sqrt{(-7)^2 - 4(2)(-15)}}{2(2)} L=7±49+1204L = \frac{7 \pm \sqrt{49 + 120}}{4} L=7±1694L = \frac{7 \pm \sqrt{169}}{4} L=7±134L = \frac{7 \pm 13}{4} This gives two possible solutions for LL: L=7+134=204=5L = \frac{7 + 13}{4} = \frac{20}{4} = 5 or L=7134=64=1.5L = \frac{7 - 13}{4} = \frac{-6}{4} = -1.5 Since length must be positive, we discard L=1.5L = -1.5. Therefore, the length is L=5L = 5 yards.

Step 4: Find the width

Substitute L=5L = 5 into the expression for the width: Width=2L7=2(5)7=107=3 yards\text{Width} = 2L - 7 = 2(5) - 7 = 10 - 7 = 3 \text{ yards}

Final Answer:

  • The length of the rectangular floor is 55 yards.
  • The width of the rectangular floor is 33 yards.

Would you like further clarification or details?

Here are 5 related questions for deeper understanding:

  1. How do you derive the quadratic formula used to solve for LL?
  2. Why is the negative solution for LL discarded in this context?
  3. What other real-life applications might require solving similar quadratic equations?
  4. How would the solution change if the total area allowed was different, say 20 square yards?
  5. Can you confirm the solution by re-checking the area with the calculated length and width?

Tip: When solving quadratic equations, always check whether both solutions are valid within the problem’s context.

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Area of a Rectangle

Formulas

Area of rectangle = length × width
Quadratic equation formula ax^2 + bx + c = 0

Theorems

Quadratic Formula

Suitable Grade Level

Grades 9-10